The Crown series 2: how much do the cast of look like the real Royal Family?

Before playing Margaret, Kirby knew almost nothing about the Queen's only sibling. "I knew that she died quite tragically, was a bit of an alcoholic, smoked a lot and had lots of affairs... but that was it," she told The Telegraph.

But after landing the part, Kirby bought "every book written about her," dedicating herself to research. "My house is full of her stuff!"

To capture her voice, the actress listened to Margaret's 1981 episode of Desert Island Discs every day during filming.